High‐altitude dust layers on Mars: Observations with the Thermal Emission Spectrometer

Abstract

[1] Limb-scanning observations of Martian atmospheric dust with the Thermal Emission Spectrometer (TES) over 3 Mars years indicate two distinct altitude layers with persistent maxima in the dust mixing ratio vertical profile. The first, lower maximum in the dust distribution profile is the "high-altitude tropical dust maximum" (HATDM) centered at 20-30 km, previously detected by the Mars Climate Sounder (MCS). Through the observation period, the HATDM followed a repeatable seasonal cycle with a brief absence in early northern spring and reached its highest altitudes and largest amplitude during the dust storm season in southern spring and summer. The HATDM is likely maintained during the day by a combination of convective and topographic updrafts and then degraded at night by scavenging from water ice clouds. The second, upper maximum in the dust distribution profile, which we refer, for convenience, to as the upper dust maximum (UDM), is centered at 45-65 km and is only detected in daytime observations. We see additional evidence of its presence in the limited number of MCS aerosol opacity retrievals available at these altitudes. Comparable dust mixing ratios are nearly absent from this altitude range at night. This upper maximum is generally a northern hemisphere phenomenon, peaking in amplitude in northern summer and nearly absent from the TES observational domain during the dust storm season. We suggest topographic updrafts over Martian volcanoes, small particle size, diurnal transport associated with thermal tides, and scavenging by water ice as probable key factors in the creation of the UDM.

Seasonal Variation in Martian Water Ice Cloud Particle Size

“…Despite our limited view of the polar (winter) atmosphere with CRISM, there is still a clear delineation between tropical clouds and polar clouds in most seasons, with a band of comparatively cloud‐free atmosphere between them. Figures and can be compared to a similar figure (Figure 17) shown by McCleese et al (; also Figure 11 of Guzewich et al, showing Thermal Emission Spectrometer limb‐viewing retrievals) which depicts the zonal average seasonal evolution of water ice clouds as viewed by the Mars Climate Sounder during Mars Year 29.…”

The impact of surface dust source exhaustion on the martian dust cycle, dust storms and interannual variability, as simulated by the MarsWRF General Circulation Model

“…Rafkin et al, 2002;Michaels et al, 2006;Goldenson et al, 2008;Davy et al, 2009;Heavens et al, 2011;Rafkin, 2012). Observations of the vertical dust distribution (Heavens et al, 2011;Guzewich et al, 2013b) indicate elevated dust maxima, suggesting a much larger amount of non-local dust mixing than predicted by MRF PBL. However, since parameterizations of deep dust injection are still under development, we continue to employ the more restricted non-local mixing allowed by the MRF PBL scheme.…”

Thermal tides during the 2001 Martian global‐scale dust storm

“…[] is that errors have been significantly reduced through accurate instrument background measurements and noise covariance matrices [ McConnochie and Smith , ] (for additional details, see Guzewich et al . [, Appendix 1]). The temperature retrieval algorithm is performed first and the aerosol opacities retrieved second.…”

“…[], which is also described in Guzewich et al . [] and appears to be a key player in the atmospheric wave response during the storm.…”